Niconico (ニコニコ) is a popular Japanese video sharing site. The site is sometimes still known by its old name, Niconico Douga (ニコニコ動画, Niconico Video), and similarly so still believed to require registration to watch any videos onsite, when access has been loosened up over the years.
Niconico has several sister sites:
Niconico Seiga (ニコニコ静画, Niconico Imageboard), an imageboard.
Niconico Nama Hosou (ニコニコ生放送, Niconico Live Streaming), a livestreaming service. Often abbreviated as ニコ生 or ニコなま.
Nicopedia (ニコニコ大百科), a wiki system. Each article also has a 2channel-like oekaki board.
A unique feature of Nicovideo is that user comments are displayed as a scrolling feed over the video. See Danmaku comments.
This tag is used for posts referencing the site itself, and locations associated with the site (such as the old Harajuku HQ), as well as for various Niconico(-adjacent) characters that have gained some fanart.
